ORBIT

The orbitals are the things that orbit around the central hub on each map. There are 8 different orbital types.

The quickest way to unlock this is:

Go to Forge mode.
Set it to 1 round.
Set the game type to Annihilate.
Select Advanced ().
Set the "Orbits" to 3.
Keep moving to the right while still on the advanced page, where you can change the orbital types. Pick three different ones.
Play the game to completion (just fly into the centre and die, doesn't matter who wins).
Repeat, but pick different orbitals each time. The orbitals are counted after each match, after you've seen all 8, *pop*.

The solar system centres/hubs do not count for this achievement and don't need to be changed.